Method for producing arylsulphonic acid isocyanates

ABSTRACT

The present invention relates to a process for preparing arylsulfonyl isocyanates by reacting an arylsulfonamide with phosgene in the presence of a catalytically effective amount of an alkyl isocyanate.

[0001] The present invention relates to a process for preparingarylsulfonyl isocyanates by reacting an arylsulfonamide with phosgene inthe presence of a catalytically effective amount of an alkyl isocyanate.

[0002] Arylsulfonyl isocyanates are industrially important intermediatesin the preparation of a large number of compounds, in particularherbicides. There is a need for processes for preparing them which notonly give a high yield and productivity but also display a high reactionrate and thus short reactor occupation times.

[0003] U.S. Pat. No. 4,379,769 describes a process for preparingarylsulfonyl isocyanates by phosgenation of arylsulfonamides in thepresence of a catalytically effective amount of an alkyl isocyanate anda catalytically effective amount of a tertiary amine base.

[0004] In Angew. Chem. 78, pp. 761-769 (1966), H. Ulrich and A. A. R.Sayigh describe the preparation of arylsulfonyl isocyanates, in whicheither a sulfonamide is reacted with a readily available alkylisocyanate to form the urea derivative and the latter is subsequentlyphosgenated, with the starting isocyanate being recovered, or else acatalytic amount of the isocyanate is added to the sulfonamide for thephosgenation.

[0005] Pestycydy 1989, (4), 1-7; ISSN: 0208-8703 describes thepreparation of 2-chlorobenzenesulfonyl isocyanate by phosgenation of thecorresponding sulfonamide in the presence of butyl isocyanats and inortho-dichlorobenzene as solvent.

[0006] Res. Discl. (1983), 23210, p. 261; ISSN: 0374-4353, describes aprocess for preparing arylsulfonyl isocyanates by phosgenation ofarylsulfonamides, in which a mixture of an alkyl isocyanate and anarylsulfonyl isocyanate is used as catalyst. The arylsulfonyl isocyanateformed as product can be recirculated to the reaction in catalyticallyeffective amounts.

[0007] Journal of Polymer Science, Vol. 13 (1975), pp. 267-268, teachesthe use of a mixture of ortho-dichlorobenzene and cellosolve acetate assolvent in the synthesis of m-phenylenedisulfonyl diisocyanates byphosgenation of m-benzenedisulfonamide in the presence of catalyticamounts of an alkyl or aryl isocyanate.

[0008] It is an object of the present invention to provide an improvedprocess for preparing arylsulfonyl isocyanates. The reaction timesinvolved should be very short and/or the formation of undesirableby-products should be minimized.

[0009] We have found that this object is achieved by reacting anarylsulfonamide with phosgene in the prescence of catalyticallyeffective amounts of an alkyl isocyanate when the reaction is carriedout in the additional presence of a catalytically effective amount of aprotic acid or a salt thereof and/or the phosgene is introduced in sucha way that the concentration of alkylarylsulfonylurea in the reactionmixture does not go below a minimum concentration during the time ofaddition.

[0010] The present invention accordingly provides a process forpreparing arylsulfonyl isocyanates by reacting an arylsulfonamide withphosgene, in which the arylsulfonamide and a catalytically effectiveamount of an alkyl isocyanate are placed in a reaction zone, forming analkylarylsulfonylurea as intermediate, and the phosgene is fed into thereaction zone, wherein

[0011] a) the reaction is carried out in the presemce of a catalyticallyeffective amount of a protic acid which has at least one hydroxy groupcapable of protolysis or a salt thereof and/or

[0012] b) the phosgene is introduced in such a way that theconcentration of alkylarylsulfonylurea in the reaction zone does not gobelow 100 ppm during the time of addition.

[0013] The process of the present invention is generally suitable forpreparing arylsulfonyl isocyanates having unsubstituted or substitutedaryl radicals. These are, for example, arylsulfonyl isocyanates of theformula I

[0014] where

[0015] R¹, R² and R³ are each, independently of one another, hydrogen orin each case substituted or unsubstituted alkyl, cycloalkyl,heterocycloalkyl, aryl or hetaryl or WCOOR^(a), WCOO⁻M⁺,

[0016] W(SO₃)R^(a), W(SO₃)⁻M⁺, WPO₃(R^(a))(R^(b)), W(PO₃)²⁻(M⁺)₂,WOR^(a), WSR^(a), (CHR^(b)CH₂O)_(x)R^(a), W-halogen, WNO₂, WC(═O)R^(a)or WCN,

[0017] where

[0018] W is a single bond, a heteroatom or a divalent bridging grouphaving from 1 to 20 bridge atoms,

[0019] R^(a), E¹, E², E³ are identical or different radicals selectedfrom among hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl andhetaryl,

[0020] R^(b) is hydrogen or C₁-C₈-alkyl, preferably methyl or ethyl,

[0021] M⁺ is a cation equivalent,

[0022] X⁻ is an anion equivalent and

[0023] x is an integer from 1 to 20,

[0024] where two adjacent radicals R¹, R² and R³ together with thecarbon atoms of the benzene ring to which they are bound may also form afused ring system having 1, 2 or 3 further rings.

[0025] For the purposes of the present invention, the expression ‘alkyl’refers to straight-chain and branched alkyl groups. These are preferablystraight-chain or branched C₁-C₂₀-alkyl groups, more preferablyC₁-C₁₂-alkyl groups and particularly preferably C₁-C₈-alkyl groups andvery particularly preferably C₁-C₄-alkyl groups. Examples of alkylgroups are, in particular, methyl, ethyl, propyl, isopropyl, n-butyl,2-butyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl,3-methylbutyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl,2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl,3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl,2,3-dimethylbutyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl,3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl,1-ethylbutyl, 2-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl,3-heptyl, 2-ethylpentyl, 1-propylbutyl, octyl, nonyl, decyl.

[0026] The expression alkyl also encompasses substituted alkyl groups.Substituted alkyl groups preferably have 1, 2, 3, 4 or 5, in particular1, 2 or 3, substituents selected from among cycloalkyl, aryl, hetaryl,halogen, NO₂ CN, acyl, carboxyl, carboxylate, —SO₃H and sulfonate.

[0027] The expression cycloalkyl encompasses unsubstituted andsubstituted cycloalkyl groups. The cycloalkyl group is preferablyC₅-C₇-cycloalkyl group such as cyclopentyl, cyclohexyl or cycloheptyl.

[0028] If the cycloalkyl group is substituted, it preferably has 1, 2,3, 4 or 5, in particular 1, 2 or 3, substituents selected from amongalkyl, alkoxy, halogen, NO₂, CN, acyl, carboxyl, carboxylate, —SO₃H andsulfonate.

[0029] For the purposes of the present invention, the expressionheterocycloalkyl encompasses saturated, cycloaliphatic groups whichgenerally have from 4 to 7, preferably 5 or 6 ring atoms and in which 1or 2 of the ring carbons have been replaced by heteroatoms selected fromamong the elements oxygen, nitrogen and sulfur and which may besubstituted. If they are substituted, these heterocycloaliphatic groupscan bear 1, 2 or 3 substituents, preferably 1 or 2 substituents,particularly preferably 1 substituent, selected from among alkyl, aryl,alkoxy, halogen, NO₂, CN, acyl, COOR^(a), COO⁻M⁺ and SO₃R^(a),preferably alkyl. Examples of such heterocycloaliphatic groups arepyrrolidinyl, piperidinyl, 2,2,6,6-tetramethylpiperidinyl,imidazolidinyl, pyrazolidinyl, oxazolidinyl, morpholidinyl,thiazolidinyl, isothiazolidinyl, isoxazolidinyl, piperazinyl,tetrahydrothiophenyl, tetrahydrofuranyl, tetrahydropyranyl, dioxanyl.

[0030] Aryl is preferably phenyl, tolyl, xylyl, mesityl, naphthyl,anthracenyl, phenanthrenyl, naphthacenyl, in particular phenyl ornaphthyl.

[0031] Substituted aryl radicals preferably have 1, 2, 3, 4 or 5, inparticular, 1, 2 or 3, substituents selected from among alkyl, alkoxy,carboxyl, carboxylate, —SO₃H, sulfonate, halogen, NO₂, CN and acyl.

[0032] Hetaryl is preferably pyrrolyl, pyrazolyl, imidazolyl, indolyl,carbazolyl, pyridyl, quinolinyl, acridinyl, pyridazinyl, pyrimidinyl orpyrazinyl.

[0033] Substituted hetaryl radicals preferably have 1, 2 or 3substituents selected from among alkyl, alkoxy, carboxyl, carboxylate,—SO₃H, sulfonate, halogen, NO₂, CN and acyl.

[0034] What has been said above with regard to alkyl, cycloalkyl andaryl radicals applies analogously to alkoxy, cycloalkyloxy and aryloxyradicals.

[0035] Halogen is preferably fluorine, chlorine, bromine or iodine,preferably fluorine, chlorine or bromine.

[0036] For the purposes of the present invention, carboxylate andsulfonate are preferably derivatives of a carboxylic acid function or asulfonic acid function, in particular a metal carboxylate or sulfonate,a carboxylic ester or sulfonic ester function or a carboxamide orsulfonamide function. They include, for example, esters withC₁-C₄-alkanols such as methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol and tert-butanol.

[0037] M⁺ is a cation equivalent, i.e. a monovalent cation or that partof a polyvalent cation which corresponds to a single positive charge. M⁺is preferably an alkali metal cation, e.g. Li⁺, Na⁺ or K⁺, or analkaline earth metal cation, NH₄ ⁺ or a quaternary ammonium compound ascan be obtained by protonation or quaternization of amines. Preferenceis given to alkali metal cations, in particular sodium or potassiumions.

[0038] X⁻ is an anion equivalent, i.e. a monovalent anion or that partof a polyvalent anion which corresponds to a single negative charge. X⁻is preferably a carbonate, carboxylate or halide, particularlypreferably Cl⁻ or Br⁻.

[0039] x is an integer from 1 to 240, preferably an integer from 3 to120.

[0040] Fused ring systems can be aromatic, hydroaromatic-and cycliccompounds joined by fusion. Fused ring systems have two, three or morerings. Depending on the way in which the rings in fused ring systems arelinked, a distinction is made between ortho-fusion, i.e. each ringshares an edge or two atoms together with each adjacent ring, andperi-fusion in which a carbon atom belongs to more than two rings. Amongfused ring systems, preference is given to ortho-fused ring systems.

[0041] The process of the present invention is particularly useful forpreparing an arylsulfonyl isocyanate of the formula I.1

[0042] where

[0043] R¹ is an electron-withdrawing group, preferably a group selectedfrom among F, Cl, Br, NO₂, CF₂H, CF₂Cl₂, CHCl₂ and CF₃, and

[0044] R² is hydrogen, C₁-C₄-alkyl, C₁-C₄-alkoxy, F, Cl, Br orC₁-C₄-alkylthio, where the alkyl radicals may bear 1, 2 or 3 halogenatoms.

[0045] The sulfonamides used as starting materials can be obtained byreacting the corresponding sulfonyl chlorides with ammonia (M.Quaedvlieg in Houben-Weyl, “Methoden der organischen Chemie”, GeorgThieme Verlag, Stuttgart, vol. 9 (1955) 398-400, F. Muth, ibid., 605ff).

[0046] The corresponding sulfonyl chlorides for preparing thesulfonamides are generally obtained by a Meerwein reaction(diazotization of suitable amides and sulfochlorinated by means ofsulfur dioxide in the presence of copper salts as catalysts: F. Muth inHouben-Weyl, “Methoden der organischen Chemie”, Georg Thieme Verlag,Stuttgart, vol. 9 (1955) 579, S. Pawlenko in Houben-Weyl, “Methoden derorganischen Chemie”, Georg Thieme Verlag, Stuttgart, vol. E 11/2 (1985)1069), from the corresponding sulfonic acids (F. Muth in Houben-Weyl,“Methoden der organischen Chemie”, Georg Thieme Verlag, Stuttgart, vol.9 (1955) 564), by chlorosulfonation of suitable aromatic precursors (F.Muth, ibid., p. 572) or by oxidative chlorination of low oxidation stagesulfur precursors (mercaptans, diaryl disulfides, S-benzylmercaptans,thiocyanates (F. Muth, ibid., p. 580, S. Pawlenko, loc. cit., p. 1073).

[0047] The reaction rate in the phosgenation of arylsulfonamides canadvantageously be increased over that in processes known from the priorart when the reaction is carried out in the presence of a catalyticallyeffective amount of a protic acid which has at least one hydroxy groupcapable of protolysis or a salt thereof.

[0048] The amount of protic acid or salt thereof used is preferably fromabout 0.05 to 1% by weight, particularly preferably from 0.1 to 0.5% byweight, based on the amount of arylsulfonamide used.

[0049] Suitable catalysts are generally compounds of carbon, nitrogen,phosphorus and sulfur which have at least one hydroxy group capable ofprotolysis and the salts thereof. The catalyst is particularlypreferably selected from among carboxylic acids, nitric acid, phosphinicacids, phosphonic acids, phosphoric acid and its monoesters anddiesters, sulfinic acids, sulfonic acids, sulfuric acid and itsmonoesters and the salts thereof.

[0050] Salts suitable as catalysts are preferably the alkali metalsalts, especially the Li, Na and K salts.

[0051] Preference is given to using an organic sulfonic acid or a saltthereof, in particular an arylsulfonic acid or a salt thereof, forcatalyzing the phosgenation. Particular preference is given to using abenzenesulfonic acid or an alkali metal salt thereof, especially sodiumbenzenesulfonate.

[0052] As an alternative to or in addition to the use of a catalyst inthe form of a protic acid or a salt thereof, the reaction rate of thephosgenation of arylsulfonamides can be increased over that ofphosgenation processes known from the prior art when the phosgene isintroduced in such a way that the alkylarylsulfonylurea concentration inthe reaction zone does not go below 100 ppm, preferably 500 ppm, duringthe time of addition.

[0053] The alkylarylsulfonylurea is formed as an intermediate in thereaction zone from the initially charged arylsulfonamide and the alkylisocyanate used as catalyst. On addition of the phosgene, theintermediate is converted into the arylsulfonyl isocyanate wanted asproduct and the alkyl isocyanate used as catalyst is reformed.

[0054] In a useful embodiment, the introduction of the phosgene iscommenced only after the alkylarylsulfonylurea concentration in thereaction zone has reached a value of 100 ppm.

[0055] In a further useful embodiment, not only the arylsulfonamide andthe alkyl isocyanate but also the alkylarylsulfonylurea derivedtherefrom are placed in the reaction zone. The amount ofalkylarylsulfonylurea initially charged is then at least 100 ppm.

[0056] In a preferred embodiment, the introduction of the phosgene iscontrolled during the time of addition so that the alkylarylsulfonylureaconcentration in the reaction zone does not go below the desired value.A volume flow which is less than the maximum volume flow is preferablyused at the beginning of the time of addition. A reduced volume flow ispreferably used during not more than the first 40% of the time ofaddition, particularly preferably during not more than the first 30%, inparticular during not more than the first 20%. The stream having a flowless than the maximum volume flow can have a flow profile which isincreased in the form of a gradient or in one or more steps to themaximum volume flow. Preference is given to using a constant volume flowwhich is less than the maximum volume flow at the beginning of the timeof addition (step profile). The volume flow employed at the beginning ofthe time of addition is preferably 60%, particularly preferably 50%, ofthe maximum volume flow. Particular preference is given to a process inwhich not more than one tenth of the total amount of phosgene isintroduced during the first sixth of the time of addition.

[0057] Preference is given to using a volume flow less than the maximumvolume flow at the end of the time of addition. A volume flow which isless than the maximum volume flow is preferably used during not morethan the last 40% of the time of addition, particularly preferablyduring not more than the last 30%, in particular during not more thanthe last 20%. The stream having a flow which is less than the maximumvolume flow can have a flow profile which is reduced from the maximumvolume flow in the form of a gradient or in one or more steps.Preference is given to using a constant volume flow which is less thanthe maximum volume flow at the end of the time of addition (stepprofile). The volume flow used at the end of the time of addition ispreferably not more than 60%, particularly preferably not more than 50%,of the maximum volume flow. Particular preference is given to a processin which not more than one tenth of the total amount of phosgene isintroduced during the last sixth of the time of addition. If thephosgene is added at a constant volume flow rate over the entire time ofaddition, the time of addition has to be significantly increased overthat in the above-described ramp procedure. Otherwise, there isappreciable formation of undesirable by-products such as arylsulfonylchlorides, which results in a decrease in the yield of isocyanates.

[0058] In a particularly preferred embodiment of the process of thepresent invention, the reaction is carried out in the presence of acatalytically effective amount of a protic acid as described above or asalt thereof and the introduction of the phosgene is also controlled asdescribed above.

[0059] The alkyl isocyanate used as catalyst is preferably selected fromamong C₄-C₁₀-alkyl isocyanates and C₅-C₈-cycloalkyl isocyanates, e.g.n-butyl isocyanate, n-pentyl isocyanate, n-hexyl isocyanate, n-octylisocyanate, n-decyl isocyanate and cyclohexyl isocyanate. Preference isgiven to using n-butyl isocyanate. The amount of alkyl isocyanate usedis preferably in the range from 5 to 40 mol %, particularly preferablyfrom 10 to 30 Mol %, based on arylsulfonamide used.

[0060] The amount of phosgene used is preferably in the range from 100to 250 mol %, particularly preferably from 150 to 200 mol %, based onarylsulfonamide used.

[0061] The phosgenation is preferably carried out at from 100 to 175° C.The pressure during the reaction is preferably ambient pressure,, butthe reaction can also be carried out at elevated or reduced pressures.

[0062] Typical reaction times are in a range from about 30 minutes to 24hours, preferably from 1 to 12 hours.

[0063] The reaction is preferably carried out in solvents which areinert toward the starting materials. Such solvents include, for example,aromatic hydrocarbons such as toluene, xylene and mesitylene,haloaromatics such as chlorobenzene, halogenated aliphatic hydrocarbonssuch as pentachloroethane, etc.

[0064] After the reaction is complete, the reaction mixture can beworked up by customary methods known to those skilled in the art. Theseinclude, for example, measures for driving off excess phosgene, forexample continued heating or passage of a gas stream, for example aninert gas, through the reaction solution. The measures employed for thework-up also include customary methods of separating off the solventused, e.g. distillation, if desired under reduced pressure. The processof the present invention gives high yields of arylsulfonyl isocyanatesand high product purities. The arylsulfonyl isocyanates obtained by theprocess of the present invention are well-suited to the preparation ofherbicides.

[0065] The invention is illustrated by the following nonrestrictiveexamples.

EXAMPLE 1

[0066] 112.6 g (0.5 mol) of 2-trifluoromethylbenzenesulfonamide, 360 mgof sodium benzenesulfonate and 9.9 g (0.1 mol) of n-butyl isocyanatetogether with 400 g of ortho-xylene are placed in a 1 l flask providedwith a reflux condenser and gas inlet tube and the mixture is heated toan internal temperature of 143° C. 12.2 g of phosgene are fed in at anessential constant volume flow over a period of 2 hours. 63.8 g ofphosgene are subsequently fed in at a maximum volume flow over a furtherperiod of 120 minutes. A further 11 g of phosgene are subsequently fedin at a constant, reduced volume flow over a period of 2 hours. Theyield of 2-trifluoromethylsulfonyl isocyanate was 85% of theory.

EXAMPLE 2 (COMPARISON)

[0067] The procedure of Example 1 was repeated, except that 87 g ofphosgene were fed in at a constant volume flow over a period of 7 hours.The formation of about 5% of 2-trifluoromethylsulfonyl chloride wasdetected by means of HPLC, and the yield of 2-trifluoromethylsulfonylisocyanate was about 80% of theory.

We claim:
 1. A process for preparing arylsulfonyl isocyanates byreacting an arylsulfonamide with phosgene, in which the arylsulfonamideand a catalytically effective amount of an alkyl isocyanate are placedin a reaction zone, forming an alkylarylsulfonylurea as intermediate,and the phosgene is fed into the reaction zone, wherein a) the reactionis carried out in the presence of a catalytically effective amount of aprotic acid which has at least one hydroxy group capable of protolysisor a salt thereof and/or b) the phosgene is introduced in such a waythat the concentration of alkylarylsulfonylurea in the reaction zonedoes not go below 100 ppm during the time of addition.
 2. A process asclaimed in claim 1, wherein a protic acid selected from among carboxylicacids, nitric acid, phosphinic acids, phosphonic acids, phosphoric acidand its monoesters and diesters, sulfinic acids, sulfonic acids,sulfuric acid and its monoesters and salts thereof is used in step a).3. A process as claimed in any of the preceding claims, wherein anorganic sulfonic acid or an alkali metal salt thereof is used in stepa).
 4. A process as claimed in any of the preceding claims, wherein aphosgene stream having a volume flow which is less than the maximumphosgene flow used is fed into the reaction zone during the first 40% ofthe time of addition.
 5. A process as claimed in any of the precedingclaims, wherein a phosgene stream having a volume flow which is lessthan the maximum phosgene flow used is fed into the reaction zone duringthe last 40% of the time of addition.
 6. A process as claimed in any ofthe preceding claims, wherein, in step b), not more than one tenth ofthe total amount of phosgene is introduced during the first sixth of thetime of addition.
 7. A process as claimed in any of the precedingclaims, wherein, in step b), not more than one tenth of the total amountof phosgene is introduced during the last sixth of the time of addition.